Following
the success of HMA No. 9, further ships were ordered by the
Admiralty. Along with the Vickers Company, three new contractors
were required to produce rigid ships. The Vickers Company had
already proven themselves with the design and construction of
No. 9 and were the only company with any experience of building
a large ship.

Following
the trials and design success of HMA No. 9, it was agreed that
the Zeppelin threat had to be tackled head on; the Admiralty required
more ships. There were initial problems at the Admiralty with
regards to change of staff and also general opinion regarding
rigid airships, as the successful non-rigid programme was expanding
rapidly. However in June of 1915, along with the Vickers Company,
three new contractors were selected to produce rigid ships.

The
three new contractors were Beardmore, Armstrong and Whitworth
and finally Shorts Brothers. All three companies were to become
famous in the world of aviation. By October 1915 the drawings
were approved and three ships were ordered. By December the pace
of design and the requirement for big ships had increased dramatically
and a further sixteen ships had been budgeted for by the Admiralty.
All of these ships were to become known as the 23 Class, which
were in effect stretched versions of the original No. 9. The designs
were seen in essence as modified versions of No.9, with an extra
bay inserted in the middle of the ship. A gun platform was added
to the top of the ship designed to take a two pound gun and two
Lewis machine guns. The platform was surrounded by 18 inch sanctions
carrying lifelines. These sanctions could be extended to double
the height in order to carry a canvas windscreen. Three other
Lewis guns were to be fitted at the extreme tail, in the control
car further aft and on the top walking way.

The bomb load was to be greater than that of HMA 9 but none was
actually specified. The ships each possessed an external keel,
to the same pattern as the No. 9. The cabin being 45 feet long
contain crew accommodation, a wireless room and a bomb room. From
the keel further aft were three gondolas which were suspended
below and accessible by open ladders.

The
ship gondolas also contained airtight buoyancy bags in case the
ships had to alight on water. This was a technical requirement
of all ships since HMA 1 - the Mayfly. With this rapid expansion
of the requirement for airship production, there were a few problems
in that so far, only one company had actually built a ship and
hence had all the facilities.

In April 1916 the Government approved for a total fleet of 10,
23 class ships, but this was later modified in the light of further
design technology available from Germany. The later ships becoming
the R23X class and the R31 class.

The
HMA 23 was the first to be completed, and hence the designation
of the class of ships. There were a number of delays in the initial
constructions and the ship was completed on 26th August 1917.
This led to the order of the R26 as Vickers had the space available
to build the ship. On lift and trim trials, the HMA 23 was found
to have a disposable lift of only 5.7 tons due to the machinery
being two tons heavier than originally estimated. Five weeks later
the HMA 25 was completed and her tests gave almost identical results.
Although not unexpected, the figures were disappointing and 2
weeks later on the 18th October the Admiralty decided that the
design must be altered. On the day of the decision the HMA 24
was also tested and found to be mysteriously two thirds of a ton
heavier than her sister ships, with a lift of only 5.1 tons. The
alterations to the ships included the removal of dynamos and bomb
frames and many other items which were deemed not necessary were
removed.

The
Admiralty ordered that modifications be carried out at once to
R.26, which was still in the early stages of construction, while
the other three ships were to be modified similarly but, of necessity,
over a longer period and slightly less drastically. The measures
to be undertaken were aimed at lightening the airships by the
elimination of all unnecessary weight. In addition to removal
of the dynamos, buffer wheels and bomb frames, many other small
items not considered essential were either taken out or replaced
with lighter equipment. The folding tables which had been intended
for the keel cabin were never installed and the original plan
of fitting a two-pounder gun on the top platform was also discarded.
The rear car was replaced by a smaller and lighter one containing
an engine with direct drive to a single two-bladed propeller 13
feet 6 inches in diameter. As there was now no space for the auxiliary
controls, these were transferred to the keel cabin.

Some of these modifications had already been carried out on the
first three ships, while others followed in due course. Together
they effected a marked, if not substantial, improvement to the
airships' performance.

R.26, on which Vickers could not begin work until No 9 had left
Barrow, arrived much later. All the recommended modifications
were incorporated in the course of her construction. Although
built more quickly than the others, in only about a year, she
did not fly until March 1918.

The last of the class was R.26. (The Admiralty decided on 18th
December 1917, that all future rigid airships should have the
prefix R before their number.) Apparently the only one of her
class to incorporate all the design changes, she was commissioned
on 22nd April 1918, and stationed at Howden. During tests she
was found to have a disposable lift of 6 1/4 tons, a top speed
of 54 mph and a ceiling of 3,500 feet. It was also discovered
that if the engines were stopped at 53 mph the speed fell to 18
mph in two minutes, so great was the drag. By the end of the year
she had flown 191 hours and 29 minutes, of which the highlights
were a flight with No 23 over London on 25th October and a patrol
of 40 hours 40 minutes on 4th/5th June, when she was commanded
by Major T . This was the longest flight yet by a British rigid,
beating No 23's previous record, set up a few days earlier, by
32 minutes. Later in the year she was transferred to Pulham and,
commanded by Major Watt, she supervised the surrender of German
submarines at Harwich on 20th November 1918.

In
January 1919, R.26 flew a further 6 hours 18 minutes, and then
had her bows specially strengthened before being experimentally
moored out in the open, using the "three wire system".
She had a tendency to assume a tail up attitude, But this was
overcome by fastening sandbags to the after guys, and she survived
for over a week without harm. Then the weather worsened, rain
soaked her envelope and a snowstorm finally beat her into the
ground. Her cars were removed, allowing her to float again, but
it was soon found that the damage she had sustained was too severe
for repairs to be worthwhile. On 24th February the order was given
for her to be scrapped and her official deletion followed on 10th
March.